Field of the Application
The disclosure is directed to wireless communications and, more particularly, to HetNet mobility management in wireless communications.
Background of the Disclosure
Wireless communication systems are widely deployed to provide various communication services, such as: voice, video, packet data, circuit-switched info, broadcast, messaging services, and so on. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, etc.). These systems can be multiple-access systems that are capable of supporting communication for multiple terminals by sharing available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless devices or terminals. In such a system, each terminal can communicate with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link can be established via a single-in-single-out (SISO), single-in-multiple-out (SIMO), multiple-in-signal-out (MISO), or a multiple-in-multiple-out (MIMO) system.
For instance, a MIMO system can employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min {NT, NR}. Each of the NS independent channels can correspond to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system can support a time division duplex (TDD) and frequency division duplex (FDD) systems. In an FDD system, the transmitting and receiving channels are separated with a guard band (some amount of spectrum that acts as a buffer or insulator), which allows two-way data transmission by, in effect, opening two distinct radio links. In a TDD system, only one channel is used for transmitting and receiving, separating them by different time slots. No guard band is used. This can increase spectral efficiency by eliminating the buffer band and can also increase flexibility in asynchronous applications. For example, if less traffic travels in the uplink, the time slice for that direction can be reduced, and reallocated to downlink traffic.
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to a mobile device. A mobile device within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, a mobile device can transmit data to the base station or another mobile device.
With the proliferation of wireless communications, the use of multiple types of access nodes may be used across a wireless network or system. Such a network or system is referred to as a HetNet (or heterogeneous network). For example, a wireless system can include larger coverage wide area networks (macrocells, base stations, evolved Node Bs, etc.) that overlay one or more, smaller local area networks (access points, microcells, picocells, femtocells, etc.). HetNets can offer wireless coverage in an environment with a wide variety of wireless coverage zones, ranging from an open outdoor environment to office buildings, homes, underground areas, and combinations of these and others. In this way, a HetNet can be considered a network with complex interoperation between macrocell, smaller cells, and in some cases WiFi network elements used together to provide a mosaic of coverage, with mobile device handoff capability between network elements.
In general, HetNet can be deployed to address one or more concerns, two of which are listed here for illustrative purposes only. First, HetNet can help increase the coverage area of a typical, or stand-alone, cell. For example, HetNet deployment helps improve coverage in hard to reach areas within the network that cannot be easily or economically served by a macrocell deployment. Second, HetNet can help increase the capacity of a typical cell. Wireless access network traffic may not be uniformly distributed throughout a network and there are generally areas within a wireless network deployment where subscribers are concentrated in small geographical area. An existing macrocell deployment may not be able to meet the capacity need of these densely subscribed areas. Such densely subscribed areas can be known as hotspots. In order to address the capacity need of hotspots, wireless operators are considering the dense deployment of small cells to meet the capacity need. The simultaneous deployment of small cells and macrocells in hotspot leads to HetNet deployment. Even though HetNet deployment helps solve capacity problem, it can introduce mobility and interference issues, to name a few.
Therefore, what are needed are techniques to help mitigate at least some of the mobility issues introduced by HetNet deployment.